Implantable medical devices are used for a wide variety of medical conditions, such as for example, cardiac pacing and sensing, cardiac rhythm management, treatments for congestive heart failure, implanted defibrillators, and neurostimulation. Neurostimulation encompasses a wide range of applications, such as for example, pain control, nervous tremor mitigation, incontinent treatment, epilepsy seizure reduction, and vagus nerve stimulation for clinical depression. These implantable medical devices generally include an implanted pulse generator that generates electrical pulses or signals that are transmitted to a targeted tissue or nerves through a therapy delivery element, such as a lead with electrodes.
Controlled placement of the therapy delivery element is required for improved therapeutic efficacy or reduced side effects. Retaining the implanted therapy delivery element in the desired location also creates difficulties because the location may change over time as the patient moves. A variety of anchors are available to prevent the therapy delivery element from migrating away from a specifically selected stimulation site.
U.S. Pat. No. 4,553,961 (Pohndorf et al.) discloses a typical suture sleeve with an outer elastomeric sleeve and an inner gripping structure. The lead is inserted though a lumen in the anchor. The gripping structure is radially compressed by the surgeon tying a suture material around the suture sleeve. The suture material causes the outer elastomeric sleeve to compress the inner gripping structure, which then collapses onto and grips the lead.
Clinicians inserting and anchoring therapy delivery elements typically prefer to perform the procedure rapidly, in a minimally invasive manner, and fix the therapy delivery element in a manner that reduces the opportunity for the therapy delivery element to migrate if practicable. Examples of some previous anchors are shown in U.S. Pat. No. 6,134,477 “Adjustable Medical Lead Fixation System” by Knuteson (Oct. 17, 2000); U.S. Pat. No. 5,484,445 “Sacral Lead Anchoring System” by Knuth (Jan. 16, 1996); and, U.S. Pat. No. 5,843,146. “Adjustable Medical Lead Anchor” by Cross, Jr. (Dec. 1, 1998).
Over-tightening of suture leads can result in lead body damage. Under-tightening can result in lead migration. Both conditions contribute to loss of stimulation and/or movement or dislodgement of the stimulation lead.